The young Briton Mark Cavendish has yet to be named as a definite starter in this year's Tour de France, which starts in London on July 7, but yesterday he was one of the first two cyclists, together with the Frenchman Sandy Casar, to sign a public anti-doping declaration that the sport's authorities hope will go a long way towards cleaning up the 2007 race.

All of the 600 cyclists who are possible starters in this year's Tour will be asked to sign the document, which will confirm that they are not currently involved in any ongoing anti-doping investigations and that they are prepared to give up their DNA if necessary so that it can be compared with the blood seized by the Spanish police during the Operation Puerto inquiry into a blood-doping ring.

Additionally, the cyclists undertake to surrender a year's salary in the event of any violation of the anti-doping rules. Christian Prudhomme, the Tour de France organiser, said yesterday that his company would if possible refuse entry to this year's Tour to any cyclists who have not signed the letter before the race starts.

The letter reads: "I swear to my team, my colleagues, the UCI [cycling's governing body], the cycling world and the public that I have not cheated, have not been involved in the Fuentes case [Operation Puerto] or in any other doping case."

The document is not legally binding but the UCI and the Tour organisers are relying on public pressure on team managers, sponsors and riders to enforce it. A list of riders who have signed will be put on the UCI's website. Pat McQuaid, the UCI president, said: "If a rider has not signed, his manager should bear that in mind when he decides whether or not to enter him in the Tour."

McQuaid said that the 6,000-page police dossier from Operation Puerto was now being examined by the UCI's lawyers in Switzerland, although it remains unclear whether its contents can be used to instigate any disciplinary proceedings.

Increasing the pressure on teams and riders, the professional teams' organisation, the AIGCP, said it would hold an extraordinary general meeting on July 5 or 6 to decide what action should be taken against any members who have violated its code of ethics. The most controversial clause in the code is one in which teams undertake not to field cyclists involved in ongoing anti-doping inquiries.

Cavendish's T-Mobile squad said yesterday that it had released last year's double Tour de France stage winner, Serhiy Honchar, for violating the team's code of conduct. Tests this spring had shown abnormalities in the Ukrainian's blood.